The purpose of this project is to characterize humoral immunity to the different serotypes of group B beta hemolytic streptococci (GBS) in pregnant women and newborn infants. Sera from normal subjects and patients with perinatal infections (endometritis, neonatal sepsis) will be studied in animal models (mouse, chick embryo), by indirect immunofluorescence, and the enzyme-linked immunosorbent assay (ELISA).